The present invention generally relates to the field of global positioning system (GPS) based navigation systems for ground vehicles such as tractors, combines, sprayers, seeders, or the like, and particularly to a inertial compensation assembly for a global positioning system based navigation system that is capable of providing inertial compensation for ground vehicle attitude over non-level or uneven terrain.
A shortcoming of global positioning system based navigation systems used in agricultural ground vehicles is that the global positioning system receiver of such systems can only determine the position of the global positioning system antenna. On most ground vehicles, the mounting location for the global positioning system antenna is constrained by the requirement that a clear view of the sky, and thus the global positioning system satellites, be provided to the antenna. Unfortunately, this position is usually not the desired control point (e.g., the hitch point of a tractor, the ground vehicle axle, a point on the ground beneath the hitch point of a tractor, or the like.) for most ground vehicle applications. Consequently, when traversing non-level terrain (e.g., terrain having a slope, hills, valleys, or the like), the global positioning system determined position and course of the ground vehicle may be incorrect, resulting in cross-track and heading errors.
In order to calculate the position of the desired control point, a precise measurement of the spatial orientation (attitude) of the ground vehicle with respect to the navigation coordinate system must be made. One approach to measuring the attitude of the ground vehicle is to mount multiple global positioning system antennas to the vehicle in a fixed, known geometry. When precision global positioning system measurements are made, the relative positions of the multiple antennas, as measured in the navigation frame, can be used to calculate the orientation (position, attitude, and course) of the entire ground vehicle. However, a navigation system employing this approach would require multiple precision global positioning system receivers and would thus be prohibitively expensive.
Alternatively, an inertial system may be used in conjunction with the global positioning system. In this approach, the inertial system determines the primary position and course information for guiding or steering the ground vehicle. Information provided by the global positioning system is then used to correct drift of the position and course information determined by the inertial system. Inertial systems include gyroscopes for measuring roll, yaw and pitch, and may include accelerometers for improving the accuracy of the information measured by the gyroscopes. Consequently, such inertial systems, like multiple antenna systems, are prohibitively expensive for many applications
Accordingly, it would be desirable to provide an inertial compensation assembly or module for a navigation system that employs inertial augmentation to compensate GPS based navigation information such as position, course, and track spacing for errors caused by variation of the ground vehicle attitude (i.e., roll and yaw) over non-level terrain, but which does not require the full suite of gyroscopes and accelerometers provided by a conventional inertial system.
The present invention is directed to an inertial compensation assembly for the navigation system of a ground vehicle, in particular an agricultural ground vehicle such as a tractor, combine, cotton picker, sprayer, or the like. The navigation system employs inertial augmentation to compensate global positioning system based navigation information such as position, course, track spacing, or the like, for errors caused by variation of ground vehicle attitude (i.e., roll and yaw) over non-level or uneven terrain. In this manner, the accuracy of the navigation system is increased without undue expense.
In accordance with a first aspect of the present invention, an inertial compensation assembly for a navigation system of a ground vehicle is disclosed. In an exemplary embodiment, the inertial compensation assembly includes a gyroscope assembly for determining a yaw angle for the ground vehicle, an accelerometer assembly for determining a lateral acceleration of the ground vehicle, and a processing system coupled to the gyroscope assembly and accelerometer assembly. The processing system uses the determined yaw angle and the lateral acceleration to correct the position and course information generated by a global positioning system receiver assembly of the navigation system employing the inertial compensation assembly, so that the position and course information used by the navigation system is inertially compensated for roll and yaw of the ground vehicle as the ground vehicle traverses non-level terrain. The processing assembly may further calculate the slope of the non-level terrain being traversed by the ground vehicle allowing the effective track spacing of an implement associated with the ground vehicle (e.g., towed by the ground vehicle or mounted to the ground vehicle) to be calculated.
In accordance with a second aspect of the present invention, a method for determining position and course information for a ground vehicle is disclosed. In an exemplary embodiment, the method includes the steps of receiving a global positioning system based position and course from a global positioning system, measuring the yaw angle for the ground vehicle using a gyroscope assembly, measuring the lateral acceleration of the ground vehicle using an accelerometer assembly, and calculating position and course information for the ground vehicle by correcting the global positioning system based position and course using the determined yaw angle and lateral acceleration so that the calculated position and course information is inertially compensated for roll and yaw of the ground vehicle as the ground vehicle traverses non-level terrain. The method may further include the step of calculating the slope of non-level terrain traversed by the ground vehicle in order to determine the effective track spacing of an implement associated with the ground vehicle (e.g., towed by the ground vehicle or mounted to the ground vehicle).
In accordance with a third aspect of the present invention, a navigation system for a ground vehicle is disclosed. The navigation system includes a global positioning system receiver assembly for receiving a positioning signal from a global positioning system and generating a global positioning system based position and course for the ground vehicle and a steering system interconnected with the global positioning system receiver assembly for steering the ground vehicle using the position and course information. An inertial compensation assembly is coupled to the global positioning system and navigation control system for determining corrected position and course information for the ground vehicle that may be utilized by the navigation control system for navigating and/or steering the ground vehicle. In an exemplary embodiment, the inertial compensation assembly includes a gyroscope assembly for determining a yaw angle for the ground vehicle, an accelerometer assembly for determining a lateral acceleration of the ground vehicle, and a processing assembly coupled to the gyroscope assembly and accelerometer assembly for determining position and course information for the ground vehicle by correcting the global positioning system position and course using the determined yaw angle and the determined lateral acceleration. The inertial compensation assembly may further calculate the slope of the non-level terrain, which is used to determine the effective track spacing of an implement associated with the ground vehicle (e.g., towed by the ground vehicle or mounted to the ground vehicle).
In accordance with a fourth aspect of the present invention, a method for determining an effective track spacing for an implement associated with a ground vehicle traversing non-level terrain (e.g., towed by the ground vehicle or mounted to the ground vehicle) is disclosed. In exemplary embodiments, the method includes the steps of determining a roll angle for the ground vehicle; ascertaining the slope of the non-level terrain using the determined roll angle; and calculating the effective track spacing, wherein the effective track spacing compensates for the slope of the non-level terrain. The ground vehicle may then be steered using the corrected track spacing so that the ground vehicle follows a track substantially parallel and tangential to a previously navigated track. In this manner, cross-track error in positioning of the implement may be reduced or eliminated.
It is to be understood that both the forgoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and together with the general description, serve to explain the principles of the invention.